Gas Cell Assembly and Applications in Absorption Spectroscopy

ABSTRACT

A gas cell assembly and applications of the gas cell assembly in absorption spectroscopy. An example gas cell assembly includes a gas cell body with an inlet for receiving a gas sample from a gas source; a first and a second end portions that allow optical transmission into and out of the body, the second end portion being substantially opposite from the first end portion; and a channel providing a path for the gas sample and optical beam(s) between the first end portion and the second end portion. The gas cell assembly also includes reflective surfaces outside the body to receive versions of the optical beams from the body and to reflect each version of the incident beam towards the body. A detector, then, receives a last reflected beam and transmits a corresponding data signal to a processing unit for analyzing the gas sample based on the data signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/737,221, filed Jun. 11, 2015, which claims foreign priority toChinese Patent Application No. 201410454301.1, entitled “Gas CellAssembly and Applications in Absorption Spectroscopy”, filed on Sep. 7,2014; Chinese Patent Application No. 201510087593.4, entitled “Gas CellAssembly and Applications in Absorption Spectroscopy”, filed on Feb. 25,2015; Canadian Patent Application No. 2,886,213, entitled “Gas CellAssembly and Applications in Absorption Spectroscopy”, filed on Mar. 24,2015; and European Patent Application No. 15169283.7, entitled “Gas CellAssembly and Applications in Absorption Spectroscopy”, filed on May 26,2015; and also claims the benefit of U.S. Provisional Application No.62/065,370, entitled “Gas Cell Assembly and Applications in AbsorptionSpectroscopy”, filed on Oct. 17, 2014. The complete disclosure of eachof U.S. patent application Ser. No. 14/737,221, Chinese PatentApplication No. 201410454301.1, U.S. Provisional Application No.62/065,370, Chinese Patent Application No. 201510087593.4, CanadianPatent Application No. 2,886,213, and European Patent Application No.15169283.7 is incorporated herein by reference.

FIELD

The described embodiments relate to a gas cell assembly and toapplications of the gas cell assembly in absorption spectroscopy.

BACKGROUND

Absorption spectroscopy is often used in the content analysis of varioussubstances. The content analysis may involve identification of thecontents in the substances and/or an amount of a particular content inthe substance.

In general, absorption spectroscopy includes spectroscopic techniquesthat measure the absorption of electromagnetic radiation as a result ofthe interaction of the electromagnetic radiation with one or morecomponents of the substance. The absorption of the electromagneticradiation is measured as a function of frequency or wavelength. Thecomponent(s) in the substance absorbs a certain amount of energy fromthe electromagnetic radiation. The intensity of the absorption variesdue to the component(s) that are present in the substance and as afunction of the frequency of the electromagnetic radiation.

SUMMARY

Various embodiments described herein generally relate to a gas cellassembly and applications of the gas cell assembly for absorptionspectroscopy.

In accordance with some embodiments, there is provided a gas cellassembly comprising: a gas cell body having an inlet for receiving a gassample from a gas source; a first end portion along a longitudinal axisof the body, the first end portion allowing optical transmission intoand out of the body, and the first end portion receiving an incidentbeam from an optical source; a second end portion substantially oppositefrom the first end portion, the second end portion allowing the opticaltransmission into and out of the body; and a channel coupled with theinlet, a length of the channel being defined by the first end portionand the second end portion, the channel providing a path for the gassample and at least the incident beam between the first end portion andthe second end portion; one or more reflective surfaces positionedoutside the body, the one or more reflective surfaces including areflective surface substantially opposite from the second end portion,the one or more reflective surfaces receiving one or more versions ofthe incident beam from the body and reflecting each version of theincident beam towards the body; and a detector operable to receive, fromone of the first end portion and the second end portion, a version of alast reflected beam, the last reflected beam being a reflected beamdirected towards the detector by the one or more reflective surfaces,the detector being operable to transmit a data signal corresponding tothe version of the last reflected beam to a processing unit foranalyzing the gas sample based on the data signal.

In accordance with some embodiments, a length of the path of theincident beam is substantially defined by, at least, a length of thechannel and a configuration of the one or more reflective surfaces, theconfiguration of the one or more reflective surfaces providing, prior tothe detector receiving the last reflected beam, at least onetransmission of a version of the incident beam within the channel and atleast one transmission of a version of the respective reflected beamwithin the channel.

In accordance with some embodiments, the one or more reflective surfacesincludes a first reflective surface substantially opposite from thefirst end portion and a second reflective surface substantially oppositefrom the second end portion; and the optical source further includes asource directing surface for receiving the incident beam from theoptical source and directing the incident beam towards the first endportion, the source directing surface being positioned substantiallybetween the first reflective surface and the first end portion.

In accordance with some embodiments, the one or more reflective surfacesincludes a first reflective surface substantially opposite from thefirst end portion and a second reflective surface substantially oppositefrom the second end portion; and the detector further includes adetector directing surface for receiving the version of the lastreflected beam from the first end portion and directing the version ofthe last reflected beam towards the detector, the detector directingsurface being positioned substantially between the first reflectivesurface and the first end portion.

In accordance with embodiments where the one or more reflective surfacesincludes a first reflective surface and a second reflective surfacesubstantially opposite from the second end portion, and the firstreflective surface being substantially opposite from the first endportion, the first reflective surface having: an optical source openingfor receiving the incident beam from the optical source and directingthe incident beam towards the first end portion; and a detector openingfor receiving the version of the last reflected beam from the first endportion and directing the version of the last reflected beam towards thedetector.

In accordance with some embodiments, the second reflective surfaceincludes at least two neighbouring reflective surfaces configured toalternately reflect the one or more versions of the incident beamtowards the body.

In accordance with embodiments where the one or more reflective surfacesinclude a first reflective surface and a second reflective surface, thefirst reflective surface being substantially opposite from the first endportion, the first reflective surface having an optical source openingfor receiving the incident beam from the optical source and directingthe incident beam towards the first end portion; and the secondreflective surface being the reflective surface substantially oppositefrom the second end portion, the second reflective surface having adetector opening for receiving the version of the last reflected beamfrom the second end portion and directing the version of the lastreflected beam towards the detector.

In accordance with some embodiments, the second reflective surface isadjustable for varying a position of the detector opening relative tothe optical source opening, the position of the detector opening varyinga number of the one or more versions of the incident beam and a numberof the respective reflected beams passing through the channel.

In accordance with some embodiments, the optical source openingincludes: a first optical source opening for receiving a first incidentbeam from the optical source; and a second optical source opening forreceiving a second incident beam from the optical source; and thedetector opening includes: a first detector opening for receiving theversion of the last reflected beam from the second end portion anddirecting the version of the last reflected beam towards the detector,the version of the last reflected beam corresponding to the firstincident beam; and a second detector opening for receiving a version ofthe second incident beam from the second end portion and directing theversion of the second incident beam towards at least one of the detectorand a reflector component for directing the version of the secondincident beam towards the detector.

In accordance with some embodiments, the optical source includes one ormore optical source components, and each of the first and secondincident beams being provided by a different optical source component.

In accordance with some embodiments, the detector includes one or moredetector components, and each detector opening being configured todirect the respective beams to a different detector component.

In accordance with some embodiments, the one or more detector componentsincludes a first detector component and a second detector componentpositioned at a different end of the gas cell assembly than the firstdetector component; the first detector opening directs the version ofthe last reflected beam towards the first detector component; and thesecond detector opening directs the version of the second incident beamtowards the reflector component, and the reflector component directs theversion of the second incident beam towards the second detectorcomponent.

In accordance with some embodiments, the second optical source openingis provided at a substantially central location of the first reflectivesurface; and the second detector opening is provided at a substantiallycentral location of the second reflective surface, the second detectoropening being positioned relative from the second optical source openingto prevent any reflection of the version of the second incident beamfrom the second reflective surface.

In accordance with some embodiments, a section of at least one of thefirst end portion and the second end portion is coupled with atemperature varying material, the temperature varying material beingcoupled to a power supply with one or more leads; and the second opticalsource opening and the second detector opening are configured forreceiving the one or more leads from the respective first end portionand second end portion.

In accordance with some embodiments, the optical source includes one ormore optical source components; and the first incident beam includes afirst multi-pass incident beam and a second multi-pass incident beam,each of the first and second multi-pass incident beams being receivedfrom a different optical source component, a path of the firstmulti-pass incident beam through the channel being radially offset froma path of the second multi-pass incident beam through the channel.

In accordance with some embodiments, the second reflective surface isadjustable for varying a position of the first detector opening relativeto the first optical source opening, the position of the first detectoropening varying a number of the one or more versions of the firstincident beam and a number of the respective reflected beams passingthrough the channel.

In accordance with some embodiments, an orientation of the first endportion relative to the first reflective surface prevents residualoptical beams at the first end portion from causing optical noise; andan orientation of the second end portion relative to the secondreflective surface prevents residual optical beams at the second endportion from causing optical noise.

In accordance with some embodiments, the first end portion is orientedat a first tilt angle with respect to the longitudinal axis of the body;and the second end portion is oriented at a second tilt angle withrespect to the longitudinal axis of the body, the second tilt anglebeing a mirror symmetry of the first tilt angle.

In accordance with some embodiments, a section of at least one of thefirst end portion and the second end portion is coupled with atemperature varying material.

In accordance with some embodiments, the temperature varying materialcomprises a heating material operable to cause a temperature of thesection of the at least one of the first end portion and the second endportion to increase.

In accordance with some embodiments, the section of the at least one ofthe first end portion and the second end portion coupled with thetemperature varying material is a substantially central location of thefirst end portion and the second end portion.

In accordance with some embodiments, the temperature varying material isshaped as one of a ring and a circle.

In accordance with some embodiments, the temperature varying material iscoupled to a power supply with one or more leads; and at least one ofthe first reflective surface and the second reflective surface has alead opening at a substantially central location, the lead openingreceiving the one or more leads.

In accordance with some embodiments, the first end portion is securablycoupled to the body for enclosing a first end of the body along thelongitudinal axis of the body; and the second end portion is securablycoupled to the body for enclosing a second end of the body, the secondend being substantially opposite from the first end.

In accordance with some embodiments, each of the first end portion andthe second end portion is securably coupled to the body with arespective seal.

In accordance with some embodiments, each of the first end portion andthe second end portion is securably coupled to the body with a threadedcoupling.

In accordance with some embodiments, each of the first end portion andthe second end portion includes a transparent section allowing theoptical transmission into and out of the body.

In accordance with some embodiments, the transparent section is formedof at least one of a glass material and a plastic material.

In accordance with some embodiments, each surface of the transparentsection is coated with an anti-reflective material.

In accordance with some embodiments, the one or more reflective surfacesincludes a mirror having a radius of curvature for the opticaltransmissions.

In accordance with some embodiments, the channel is substantiallyenclosed by a temperature varying material operable to vary atemperature of the gas sample.

In accordance with some embodiments, the temperature varying materialincludes a heating material operable to cause a temperature of the gassample to be above an ambient temperature of a surrounding of the gascell assembly.

In accordance with some embodiments, the temperature varying materialincludes a cooling material operable to cause a temperature of the gassample to be below an ambient temperature of a surrounding of the gascell assembly.

In accordance with some embodiments, the temperature varying material isoperable to vary the temperature of the gas sample to a user-specifiedvalue.

In accordance with some embodiments, the incident beam includes acollimated beam.

In accordance with some embodiments, the gas cell body further includesan outlet for releasing the gas sample from the channel.

In accordance with some embodiments, the processing unit is configuredto conduct an absorption spectroscopy analysis of the gas sample basedon the data signal received from the detector.

In accordance with some embodiments, a wavelength of the incident beamvaries according to the absorption spectroscopy analysis being conductedon the gas sample.

In accordance with some embodiments, use of an embodiment of the gascell assembly described herein is provided for conducting an absorptionspectroscopy measurement of a gas sample.

In accordance with some embodiments, there is provided an absorptionspectroscopy system including: an optical source for transmitting anincident beam; a gas cell assembly having: an inlet for receiving a gassample from a gas source; a channel coupled with the inlet, the channelproviding a path for at least the incident beam and the gas sample; anda detector positioned relative to the channel for receiving a lastreflected beam corresponding to a version of the incident beam, thedetector being operable to transmit a data signal corresponding to thereflected beam; an absorption spectroscopy analyzer in electroniccommunication with the gas cell assembly, the analyzer comprising: acommunication module operable to receive the data signal from thedetector; and a processing module operable to conduct the absorptionspectroscopy analysis of the gas sample based on the data signal; and acontroller module in electronic communication with the absorptionspectroscopy analyzer and the gas cell assembly, the controller modulebeing configured to receive control signals from the absorptionspectroscopy analyzer.

In accordance with some embodiments, the absorption spectroscopy systemincludes an embodiment of the gas cell assembly described herein.

In accordance with some embodiments, the outlet is coupled to a pump,the pump being operable to direct a movement of the gas sample from thegas source into the inlet and out of the outlet. The pump, may, in someembodiments be a jet pump.

In accordance with some embodiments, the inlet is coupled to the gassource with a sampling tube, the sampling tube being inserted into avent opening of the gas source.

In accordance with some embodiments, a filter is provided within thesampling tube, the filter interacting with an initial gas sample fromthe gas source to remove contaminants from the initial gas sample forgenerating the gas sample.

In accordance with some embodiments, a filter is located outside thevent opening, the filter interacting with an initial gas sample from thegas source to remove contaminants from the initial gas sample forgenerating the gas sample.

In accordance with some embodiments, the filter includes a ceramicfilter.

In accordance with some embodiments, the inlet is coupled to thesampling tube with a multi-directional valve, the multi-directionalvalve is operable by the controller module in a first position forproviding a path between the gas source and the inlet, and in a secondposition for providing a path between an external gas line and the gassource.

In accordance with some embodiments, the controller module operates themulti-directional valve in the second position in response to a controlsignal from the absorption spectroscopy analyzer indicating the filteris to be cleaned, the path between the external gas line and the gassource directing a pressurized gas from the external gas line towardsthe filter.

In accordance with some embodiments, the system described hereinincludes a pressure measuring device coupled to the inlet, the pressuremeasuring device monitoring a gas pressure of the gas sample within thegas cell assembly; and a first valve operable by the controller moduleto provide a path between an external gas line and the filter inresponse to an activation signal generated by the pressure measuringdevice, the activation signal being generated by the pressure measuringdevice when the pressure measuring device determines the gas pressure isless than a minimum pressure threshold.

In accordance with some embodiments, the gas source is a powergeneration plant.

In accordance with some embodiments, the absorption spectroscopyanalyzer is in electronic communication with the gas cell assembly viaat least one of (i) one or more fiber optic cables and (ii) one or morecoaxial cables.

In accordance with some embodiments, the controller module includes arelay circuitry.

BRIEF DESCRIPTION OF THE DRAWINGS

Several embodiments will now be described in detail with reference tothe drawings, in which:

FIG. 1 is a block diagram of components interacting with a gas cellassembly in accordance with an example embodiment;

FIG. 2A is a cross-sectional view of an example gas cell assembly;

FIG. 2B is a cross-sectional view of another example gas cell assembly;

FIG. 2C is a cross-sectional view of a further example gas cellassembly;

FIG. 2D is a cross-sectional view of the gas cell assembly of FIG. 2C inaccordance with another example embodiment;

FIG. 3 is a front view of a reflective surface in accordance with anexample embodiment;

FIG. 4A is a front view of an end portion of a gas cell assembly inaccordance with an example embodiment;

FIG. 4B is a front view of a reflective surface in accordance withanother example embodiment;

FIG. 5A is a cross-sectional view of yet another example gas cellassembly;

FIG. 5B is a cross-sectional view of another example gas cell assembly;

FIG. 5C is a front view of an example first reflective surface for thegas cell assembly of FIG. 5A;

FIG. 5D is a front view of an example first reflective surface for thegas cell assembly of FIG. 5B;

FIG. 6A is a perspective view of a gas cell assembly in accordance withanother example embodiment;

FIG. 6B is a perspective view of a gas cell assembly in accordance withyet another example embodiment;

FIG. 7A is a front view of an example reflective surface for the gascell assembly of FIGS. 6A and 6B;

FIG. 7B is a front view of another example reflective surface for thegas cell assembly of FIGS. 6A and 6B;

FIG. 8 illustrates an example absorption spectroscopy system involvingthe gas cell assembly of FIG. 2D in accordance with an exampleembodiment; and

FIG. 9 illustrates another example absorption spectroscopy systeminvolving the gas cell assembly of FIG. 2D in accordance with anotherexample embodiment.

The drawings, described below, are provided for purposes ofillustration, and not of limitation, of the aspects and features ofvarious examples of embodiments described herein. For simplicity andclarity of illustration, elements shown in the drawings have notnecessarily been drawn to scale. The dimensions of some of the elementsmay be exaggerated relative to other elements for clarity. It will beappreciated that for simplicity and clarity of illustration, whereconsidered appropriate, reference numerals may be repeated among thedrawings to indicate corresponding or analogous elements or steps.

DESCRIPTION OF EXAMPLE EMBODIMENTS

It will be appreciated that numerous specific details are set forth inorder to provide a thorough understanding of the example embodimentsdescribed herein. However, it will be understood by those of ordinaryskill in the art that the embodiments described herein may be practicedwithout these specific details. In other instances, well-known methods,procedures and components have not been described in detail so as not toobscure the embodiments described herein. Furthermore, this descriptionand the drawings are not to be considered as limiting the scope of theembodiments described herein in any way, but rather as merely describingthe implementation of the various embodiments described herein.

It should be noted that terms of degree such as “substantially”, “about”and “approximately” when used herein mean a reasonable amount ofdeviation of the modified term such that the end result is notsignificantly changed. These terms of degree should be construed asincluding a deviation of the modified term if this deviation would notnegate the meaning of the term it modifies.

In addition, as used herein, the wording “and/or” is intended torepresent an inclusive-or. That is, “X and/or Y” is intended to mean Xor Y or both, for example. As a further example, “X, Y, and/or Z” isintended to mean X or Y or Z or any combination thereof.

It should be noted that the term “coupled” used herein indicates thattwo elements can be directly coupled to one another or coupled to oneanother through one or more intermediate elements.

Optical absorption spectroscopy is an example of absorption spectroscopyand involves directing an optical beam from an optical source throughthe substance. The substance may be in an enclosure or an open path. Thesubstance may be a gas, for example. As noted, the intensity of theabsorption varies, at least, due to the different components that may bepresent in the substance. The transmitted optical beam is received by adetector, which can then provide a data signal related to thetransmitted optical beam to an analyzer device for conducting therelevant absorption spectroscopy analysis.

The absorption of the electromagnetic radiation at a specific frequencyby the substance can generally be quantified by the Beer-Lambert law:

I=I_(o)e^(−kcL)

where “I” represents an intensity of the detected optical beam, “I_(o)”represents an intensity of the initial optical beam provided by theoptical source, “k” represents an absorptivity of an attenuator in thesubstance at a given temperature and frequency, “c” represents aconcentration of the attenuator in the substance and “L” represents apath length of the optical beam through the absorbing substance.According to the Beer-Lambert law, the intensity of the detected opticalbeam (I) is generally inversely proportional to the path length, L,since the absorption by the substance increases as the path lengthincreases. The inverse proportionality between the detected intensityand the path length applies especially for components within thesubstance that are either present at very low levels or particularlyweak absorbers or both. The increased absorption can increase thesensitivity of the absorption spectroscopy analysis and, therefore,increasing the path length can be advantageous.

The sensitivity at which the contents can be identified is increasinglyimportant in certain industries. Coal-burning power plants, for example,are becoming more regulated by the relevant regulatory bodies in termsof mono-nitrogen oxides (NO_(x)) emissions. The ability to accuratelyidentify the contents of the substances so that appropriate feedback canbe sent by the relevant control systems can therefore be critical.

The absorption of electromagnetic radiation by the substance can eitherbe made in-situ (that is, the electromagnetic radiation is passedthrough the substance at the location where the substance is formed) orextractive (that is, the electromagnetic radiation is passed through thesubstance after the substance is extracted from its original locationand brought into a measurement environment, such as a closed container).Typically, extractive absorption spectroscopy measurements are performedusing an absorption cell, or a gas cell, of a suitable length. A lengthof the gas cell is generally restricted by practical limitations, suchas portability of the gas cell and space availability at the measurementsite. Multi-pass gas cells can be used for providing an increased pathlength that can usually improve absorption detection sensitivity withoutsignificantly increasing the size of the measurement instrument. Themulti-pass gas cells typically include a set of mirrors that is exposedto the gas sample. The set of mirrors reflects the optical beam multipletimes so that the path length of the optical beam through the absorbingsubstance increases substantially without needing to increase the lengthof the gas cell itself.

However, during operation of the gas cell and in particular inindustrial settings, even if the gas is filtered, dust and/or othercontaminants are often drawn into the gas cell. Over time, the dust andcontaminants become deposited on the mirrors, and depending on the typeof the contaminant, the contaminants may even react with the surfaces ofthe mirror. As a result, the reflectivity of the mirrors can degradeover time. It is possible that the deterioration of the mirrors can becompensated with software but will nevertheless cause a reduction in thesensitivity of the detected intensity of the optical beam. The purposeof using the multi-pass cell to increase the path length in order toincrease the sensitivity of the absorption data can, therefore, bedefeated. Instead, it is likely that the mirrors need to be dismantledto be cleaned or replaced. The dismantling process can be particularlycumbersome since the mirrors need to be carefully aligned.

Also, the gas cell may be required to be operated at a temperature thatis well above ambient for several reasons. First, certain undesiredchemicals tend to react at lower temperatures and affect the compositionof the substance. The undesired chemicals may also react to formcontaminants that can degrade the components of the measurementinstrument. For example, in coal-burning power plants, ammonia is ofteninjected into the resulting flue gas to reduce NO_(x) emissions.However, over-injection of the ammonia may result in ammonia slip, orexcess ammonia, within the flue gas. Depending on the temperature of theflue gas, the excess ammonia and the sulfur compounds formed during thecombustion of coal can react to form ammonium bisulfate (ABS). At coolertemperatures, ABS formation can clog filters and cloud mirrors andwindows of the gas cell. Second, higher temperatures may be required toprevent condensation in the gas cell from obscuring the optical beam.

The high temperature that may be required can also make the alignment ofthe optical components very difficult. Temperature changes can affectthe alignment and, therefore, optical alignment needs to be performedwhen the gas cell has reached the temperature at which it will operate.

As noted, gas cells are often used for absorption spectroscopy analysis.The absorption amount and, correspondingly, the sensitivity of theabsorption spectroscopy analysis can depend on a path length of thetransmission of an optical beam through a sample being tested, which canbe referred to as a gas sample.

Different multi-pass gas cells have been developed for increasing thepath length. Common types of multi-pass cells can include gas cellsbased on the Herriott and White designs.

The Herriott gas cell includes two mirrors with identical focal lengthand the two mirrors are separated from each other by a distance, “D”.The mirrors can have various forms, such as spherical, astigmatic orother complex forms. The mirrors within the Herriott gas cell areusually enclosed in a suitable container with inlet and outletconnections to allow the sample gas to flow through the gas cell at therequired rate. The container used in the Herriott gas cell is usuallyconfigured to allow entry and exit of optical beams.

The White gas cell includes three spherical and concave mirrors with thesame radius of curvature. Two neighbouring mirrors can be providedacross from the third mirror. One of the neighbouring mirrors can beconfigured for receiving at least an incident beam from the opticalsource, and the other neighbouring mirror can be configured for, atleast, directing the last reflected beam towards the detector. Duringthe transit of the versions of the incident beam within the White gascell, the neighbouring mirrors can alternately reflect the versions ofthe incident beam received from the third mirror. Similar to theHerriott gas cell, the mirrors in the White gas cell are also typicallyenclosed in a suitable container with inlet and outlet connections toallow the sample gas to flow through the gas cell.

However, as noted, the mirrors in the example multi-pass gas cells, suchas the Herriott gas cell and the White gas cell, are in direct contactwith the gas sample and are therefore, subject to any dust and/orcontaminants that may be in the sample. Depending on the environment,the gas sample may include corrosive contents causing corrosion in themeasurement components, such as the mirrors, of the gas cell.

Reference is first made to FIG. 1, which is a block diagram 2 ofcomponents interacting with an example gas cell assembly 10. The gascell assembly 10 has, at least, an inlet 22 i and an outlet 22 o. Theinlet 22 i and outlet 22 o may be closed to contain the gas samplewithin the gas cell assembly 10. As shown, the gas cell assembly 10 canreceive an incident beam 50 emitted from an optical source 12. Theincident beam 50 is transmitted within the gas cell assembly 10 and aversion of the incident beam 50 is received by a detector 24.

Generally, although not shown in FIG. 1, the gas cell assembly 10includes a gas cell body enclosed at a first end and a second end by arespective first end portion and a second end portion. Each of the endportions includes an optical permeable component that allows opticaltransmission into and out of the gas cell body, while containing the gassample within the cell body. One or more reflective surfaces can belocated substantially opposite from one of the end portions. Thereflective surfaces, therefore, are not in contact with the gas sample.Embodiments of the gas cell assembly 10 will be described with referenceto FIGS. 2A to 2D, 5A, 5B and 6A.

As shown in FIG. 1, the inlet 22 i of the gas cell assembly 10 isoperatively coupled with a gas source 18 to receive the gas sample. Thedetector 24 can also be in electronic communication with a computingdevice 16 for receiving a data signal containing data associated withthe transmitted optical beam. The data associated with the transmittedoptical beam may include optical data. The gas cell assembly 10 can alsobe in electronic communication with a controller module 14 for receivingcontrol signals associated with the operation of the gas cell assembly10.

When the detector 24 receives the data signal in the form of an opticalsignal, the detector 24 can convert the optical signal to an electricalsignal. For example, the detector 24 can determine a current value thatis proportional to the intensity of the transmitted optical beamreceived by the detector 24. The detector 24 may then provide theelectrical signal to the computing device 16 via a connector, such as acoaxial cable. In some embodiments, the detector 24 may convert theelectrical signal to another form, such as an optical signal using anelectrical to optical signal converter. The resulting optical signal canbe provided to the computing device 16 via fiber optic cables.

The detector 24 may, in some embodiments, include multiple detectorcomponents that are configured for receiving different data signals. Forexample, the detector 24 may include a first detector component fordetermining an intensity of a first optical beam and a second detectorcomponent for determining an intensity of a second optical beam that isdifferent from the first optical beam. The various detector componentsmay be arranged together in one unit or provided as physically separateunits.

The optical source 12 is positioned relative to the gas cell assembly 10for transmitting the incident beam 50 towards a gas cell body (notshown) containing the gas sample. A wavelength of the incident beam 50can vary depending on the type of absorption spectroscopy analysis to beconducted and on the gas sample to be measured. That is, the wavelengthmay vary according to the content that is intended to be identified. Forexample, near or mid-infrared beams can be used for measuring variousdifferent types of gases, such as very low levels of ammonia gas. Forcertain other gases, visible and/or ultra-violet (UV) beams may also beused. The incident beam 50 may, in some embodiments, be a collimatedbeam.

The optical source 12 may include an optic generator for generating theincident beam 50 or may include launching optics that receive theincident beam 50 from a remote optic generator via fiber-optic cables.

For example, when the optical source 12 includes launching optics, theoptic generator may be provided at the computing device 16. In someembodiments, the optic generator may include a tunable diode laser thatis located at the computing device 16, which may be an opticalspectroscopy analyzer. The incident beam 50 may therefore be a laserbeam that is provided from the tunable diode laser to the optical source12 via a fiber-optic cable that can support the wavelength of the laserbeam.

Similar to the detector 24, the optical source 12 may include multipleoptical source components that are configured for transmitting differentincident beams 50. For example, the optical source 12 may include afirst optical source component for transmitting a first incident beamand a second optical source component for transmitting a second incidentbeam. The various optical source components may be arranged together inone unit or provided as physically separate units. As will be described,the gas cell assembly 10 may receive multiple different incident beams50 for identifying and/or measuring different gas components within thegas sample.

The gas source 18 can vary depending on the test environment. Forexample, in power generation plants, the gas source 18 may be a ventopening of a pipeline or a duct. In laboratory test environments, thegas source 18 may be an experimental gas formed from a reaction orcontaminant. In chemical plants, the gas source 18 may be a process gas.In combustion applications, the gas source 18 may be an off-gas such ascarbon monoxide and/or carbon dioxide. In incinerators, the gas source18 may be a stack where, for example, hydrogen chloride needs to bemeasured. It will be understood that various different gas sources 18may be used with the gas cell assemblies 10 described herein.

The computing device 16, as described, is operable to receive datasignals from the detector 24 for conducting the relevant analysis on theinformation provided by the data signals. For example, the computingdevice 16 may include or may be an absorption spectroscopy analyzer forconducting an absorption spectroscopy analysis on the informationprovided by the data signals. The computing device 16 may include anelectronic tablet device, a personal computer, workstation, server,portable computer, mobile device, personal digital assistant, laptop,smart phone, portable electronic devices, measurement instrument, or anycombination of these. An optical source 12 may also be provided as partof the computing device 16. For example, the incident beam 50 from theoptical source 12 can be transmitted from the computing device 16 (whichmay be located at a different location from the gas cell assembly 10)via a fiber-optic cable.

The computing device 16 can include, at least, a communication module 26and a processing module 28. It should be noted that in alternativeembodiments, the communication module 26 and the processing module 28may be combined or may be separated into further modules. Furthermore,the communication module 26 and the processing module 28 may beimplemented using software, hardware, or a combination of software andhardware.

The communication module 26 is operable to receive the data signals fromthe detector 24. The communication module 26 may include at least one ofa serial port, a parallel port or a USB port. The communication module26 may also include at least one of an Internet, Local Area Network(LAN), Ethernet, Firewire, modem, or other wireless connections. Variouscombinations of these elements may be incorporated within thecommunication module 26.

The processing module 28 is operable, at least, to conduct the relevantanalysis based on the data signals received by the communication module26, or may, in some embodiments, cause the relevant analysis to beconducted by one or more other modules (not shown). The processingmodule 28 may be any suitable processors, controllers or digital signalprocessors that can provide sufficient processing power depending on theconfiguration, purposes and requirements of the computing device 16. Insome embodiments, the processing module 28 can include more than oneprocessor with each processor being configured to perform differentdedicated tasks.

In some embodiments, the computing device 16 may also include a storagemodule (not shown). The storage module can include RAM, ROM, one or morehard drives, one or more flash drives or some other suitable datastorage elements such as disk drives, etc. The storage module may beinternal to the computing device 16 or separate from the computingdevice 16 but in electronic communication with the computing device 16.

The controller module 14 can be in electronic communication with thecomputing device 16 and the gas cell assembly 10. Accordingly to theanalysis of the information provided by the data signals, the computingdevice 16 can generate corresponding control signals for the controllermodule 14. The control signals can indicate to the controller module 14that the operation of the gas cell assembly 10 should be varied. Examplecontrol signals will be described with reference to FIG. 8.

In some embodiments, the controller module 14 can include a relaycircuitry.

In some embodiments, one or more of the gas cell assembly 10, thecomputing device 16 and the controller module 14 may be configured tocommunicate via a network (not shown) capable of carrying data. Anexample network may be the Internet, Ethernet, coaxial cable, fiberoptics, satellite, mobile, wireless fixed line, local area network, widearea network, and others, including any combination of these, capable ofinterfacing with, and enabling communication between the variouscomponents.

Various embodiments of the gas cell assembly 10 will now be describedwith reference to FIGS. 2A to 2D, 5A, 5B and 6A.

FIG. 2A is a cross-sectional view of a gas cell assembly 100A.

The gas cell assembly 100A includes a gas cell body 102 having an inlet104 i, an outlet 104 o, a channel 106, a first end portion 108 f and asecond end portion 108 s. Each of the inlet 104 i, the outlet 104 o, thefirst end portion 108 f and the second end portion 108 s is coupled withthe channel 106. The gas cell body 102 is mounted to a base 132 with twogas cell body mounts 130 a, 130 b. It will be understood that othernumber of gas cell body mounts 130 may similarly be used for mountingthe gas cell body 102 to the base 132.

The inlet 104 i can receive the gas sample from the gas source 18 andthe outlet 104 o can release the gas sample from the channel 106.

The first end portion 108 f is provided along a longitudinal axis of thegas cell body 102, and the second end portion 108 s is substantiallyopposite from the first end portion 108 f. The separation between thefirst end portion 108 f and the second end portion 108 s can define alength of the channel 106, as shown in FIG. 2A. The length of thechannel 106 generally corresponds to the length of the gas cell assembly100A.

Each of the first and the second end portions 108 f and 108 s can besecurably coupled to the gas cell body 102 for enclosing a respectivefirst end and second end of the gas cell body 102. The secured couplingmay include a seal, such as o-rings, and/or a threaded coupling. Othertypes of couplings may similarly be used.

Each of the first and the second end portions 108 f and 108 s can allowoptical transmission into and out of the gas cell body 102. In someembodiments, each of the first and the second end portions 108 f and 108s can include a transparent section for allowing optical transmissioninto and out of the gas cell body 102. The transparent section should beformed of such materials that can minimize penetration losses as much aspossible. An anti-reflection material may be applied to, or coated onto,each surface of the optically transparent sections to minimizereflection losses. The transparent section may be formed of a glassmaterial, a plastic material and/or other suitable materials.

As shown in FIG. 2A, the first end portion 108 f can receive theincident beam 50 from the optical source 112. The optical source 112 ismounted to the base 132 with a mount 126. The mount 126 is also coupledwith two alignment controls 122 a and 122 b for aligning the opticalsource 112 with respect to the first end portion 108 f and a reflectivesurface 110 opposite from the second end portion 108 s. The alignmentcontrols 122 a, 122 b may be a screw and/or other components operable toadjust an orientation of the optical source 112.

The reflective surface 110 is positioned outside the gas cell body 102.As shown in FIG. 2A, the reflective surface 110 can be mounted to thebase 132 with a mount 124. The mount 124 can also be coupled with twoalignment controls 116 and 118 for aligning the reflective surface 110with respect to the second end portion 108 s and the optical source 112.The two alignment controls 116, 118, like the alignment controls 122 a,122 b, may also be a screw and/or other similar components that areoperable to adjust an orientation of the reflective surface 110. Thereflective surface 110 may be a mirror, such as a concave mirror.

When an optical beam is received at the reflective surface 110, thereflective surface 110 can reflect the optical beam, or the reflectedbeam 52, towards the second end portion 108 s. As shown in FIG. 2A, thereflected beam 52 is received at a location of the second end portion108 s that is different from a location from which the optical beam wastransmitted (a prior transmission location). The prior transmissionlocation on the second end portion 108 s is a location that previouslytransmitted an optical beam towards the reflective surface 110.Generally, the location at which the reflected beam 52 is received atthe second end portion 108 s varies, at least, according to an angle ofincidence of the optical beam and a curvature of the reflective surface110.

In the described embodiments, the second end portion 108 s can beoriented relative to the reflective surface 110 and the longitudinalaxis of the gas cell body 102. For example, as shown in FIG. 2A, thesecond end portion 108 s can be tilted towards the reflective surface110 with respect to the longitudinal axis of the gas cell body 102. Theconfiguration of the end portions 108 relative to the reflectivesurfaces 110 described herein can minimize optical noise (etalons).

Generally, when an optical transparent component receives an opticalbeam, a small amount of the optical beam, or a residual reflection, maybe reflected by the optical transparent component since the opticaltransparent section may act as a relatively weak reflective surface.Anti-reflection material can, to an extent, minimize the residualreflection at the optical transparent component. However, it isnevertheless still possible for the optical transparent component togenerate some amount of residual reflection upon receiving the opticalbeam. For the gas cell assemblies 10 described herein, if the endportions 108 and the reflective surfaces 110 were not oriented in thedescribed configurations, the end portions 108 may generate a residualreflection upon receiving a reflected beam from the reflective surface110. The residual reflection may then arrive at the reflective surface110 and cause an undesired series of optical beams, or optical noise(etalons). The optical noise may eventually reach the detector 114 andaffect the data signals received by the detector 114.

Referring again to FIG. 2A, by orientating the second end portion 108 swith respect to the reflective surface 110 and the longitudinal axis ofthe gas cell body 102 in certain configurations, the residualreflections may be minimized. For example, by tilting the second endportion 108 s at a certain tilt angle with respect to the longitudinalaxis of the gas cell body 102 and the reflective surface 110, theresidual reflections that may result are prevented from being receivedby the reflective surface 110.

The tilt angle of each of the first and second end portions 108 f, 108 scan generally be equal to each other and have a mirror symmetry witheach other so that the optical beam does not deviate from the path. Thatis, when an optical beam is received at the first end portion 108 f anddeviated (e.g., shifted) from the optical path by the tilt angle of thefirst end portion 108 f, the transmitted beam received at the second endportion 108 s can be realigned to the optical path by the tilt angle ofthe second end portion 108 s. Therefore, the tilt angles at each of therespective first and second end portions 108 f and 108 s compensate foreach other.

When the incident beam 50 is received at the first end portion 108 f, aversion of the incident beam 50 is transmitted towards the second endportion 108 s while interacting with the gas sample inside the channel106. The version of the incident beam 50 enters the channel 106 insteadof the original incident beam 50 due to possible reflection losses atthe first end portion 108 f. At the second end portion 108 s within thechannel 106, another version of the incident beam 50, or a secondversion of the incident beam 50, is directed towards the reflectivesurface 110. The second version of the incident beam 50 is furtherreduced due to absorption by the gas sample while inside the channel 106and possible reflection losses at the second end portion 108 s.

In some embodiments, an anti-reflective material may be added, orcoated, to one or both surfaces of each of the first end portion 108 fand/or the second end portion 108 s. The anti-reflective material canreduce undesirable reflections that may occur at the first end portion108 f and the second end portion 108 s. The anti-reflective material mayvary for different wavelengths of the optical beam and/or an angle ofincidence of the optical beam. An example embodiment with theanti-reflective material will be described with reference to FIG. 2D.

The reflective surface 110 can receive the second version of theincident beam 50 and then transmits a reflected beam 52 towards thesecond end portion 108 s. The reflected beam 52 is then transmittedthrough the second end portion 108 s through the channel 106 towards thefirst end portion 108 f. The first end portion 108 f then transmits aversion of the reflected beam 52, or a last reflected beam 54, towardsthe detector 114 coupled to the mount 126. Therefore, with the gas cellassembly 100A, the various versions of the incident beam 50, combined,travel a total path length of, at least, twice the length of the channel106 before the last reflected beam 54 is received by the detector 114.The sensitivity of the absorption measurement, therefore, is increaseddespite the channel 106 not having increased in length.

Also, the reflective surface 110 is not exposed to the gas sample and,therefore, will not be subjected to any contaminants and/or dust thatmay be present in the gas sample. Instead, the sides of the first andthe second end portions 108 f and 108 s facing the interior of thechannel 106 is exposed to the gas sample. As described, the first andthe second end portions 108 f and 108 s can be formed of at least atransparent section to allow optical transmission into and out of thegas cell body 102. The positions of the first and the second endportions 108 f and 108 s, therefore, do not affect the optical alignmentbetween the reflective surface 110 and the optical source 112.Therefore, the first and the second end portions 108 f and 108 s can beremoved from the channel 106 for cleaning or to be replaced withoutaffecting the alignment of the optical components, namely the reflectivesurface 110 and the optical source 112.

FIG. 2B is a cross-sectional view of another gas cell assembly 100B.

Unlike the gas cell assembly 100A of FIG. 2A, the gas cell assembly 100Bincludes two reflective surfaces, namely a first reflective surface 110f and a second reflective surface 110 s. The first reflective surface110 f is positioned between the optical source 112 and the first endportion 108 f, and is mounted to the base 132 with a first mount 124 f.Alignment controls 116 f and 118 f are also coupled to the first mount124 f and are operable for adjusting an orientation of the firstreflective surface 110 f with respect to the first end portion 108 f andthe second reflective surface 110 s.

The first end portion 108 f can be oriented relative to the firstreflective surface 110 f similar to the relative orientation of thereflective surface 110 and the second end portion 108 s of the gas cellassembly 100A of FIG. 2A. For example, as illustrated in FIG. 2B, thefirst end portion 108 f may be tilted with respect to the longitudinalaxis of the gas cell body 102. The second reflective surface 110 s andthe second end portion 108 s may be similarly oriented, but having amirror symmetry, relative to each other.

The second reflective surface 110 s is similar to the reflective surface110 of FIG. 2A. The second reflective surface 110 s is mounted to thebase 132 with a second mount 124 s. Alignment controls 116 s and 118 sare also coupled to the second mount 124 s for adjusting an orientationof the second reflective surface 110 s with respect to the second endportion 108 s and the first reflective surface 110 f.

With the first and second reflective surfaces 110 f and 110 s, anoptical beam can be transmitted multiple times through the channel 106before being directed towards the detector 114. As shown in FIG. 2B, theincident beam 50 can be provided by the optical source 112. The firstreflective surface 110 f can include an optical source opening forreceiving the incident beam 50.

For example, as shown in FIG. 3, an example reflective surface 210 caninclude an opening 214 through which an optical beam 216 can betransmitted. The opening 214 may be the optical source opening in someembodiments. As shown, the opening 214 can be provided at approximatelythe outer perimeter of the reflective surface 210, and sized tofacilitate a diameter of the optical beam.

Referring again to FIG. 2B, the optical source opening (not shown)allows for the incident beam 50 to be directed towards the first endportion 108 f. As described with reference to FIG. 2A, a version of theincident beam 50 in FIG. 2B then travels through the channel 106 towardsthe second end portion 108 s. A second version of the incident beam 50is received at the second reflective surface 110 s. A first reflectedbeam 52 is then generated by the second reflective surface 110 s as aresult of receiving the second version of the incident beam 50. Thefirst reflected beam 52 is then directed towards the second end portion108 s and a version of the first reflected beam 52 is received at thefirst reflective surface 110 f.

Unlike the gas cell assembly 100A of FIG. 2A, the inclusion of the firstand second reflective surfaces 110 f and 110 s into the gas cellassembly 100B enables multiple reflections of the optical beam prior tothe detector 114 receiving the last reflected beam 54. The number ofreflections that may be provided by the gas cell assembly 100B can varydepending on a configuration (e.g., orientation, curvature, etc.) andseparation of the reflective surfaces 110 s, 110 f. In the example ofFIG. 2A, as shown, the first reflective surface 110 f generates a secondreflected beam 52′, which is directed through the channel 106 towardsthe second reflective surface 110 s. A third reflected beam 52″ isgenerated by the second reflective surface 110 s and is directed towardsthe gas cell body 102. A version of the third reflected beam 52″, or thelast reflected beam 54, is eventually directed through the first endportion 108 f towards the detector 114 via a detector opening (notshown).

The detector opening may, in some embodiments, be the same as theoptical source opening. The common opening 214, therefore, can be sizedto facilitate the diameter of the incident beam 50 and the lastreflected beam 54. The incident beam 50 received from the optical source112 can have a different angle from the last reflected beam 54 and,therefore, the detector 114 can be located relative to the opening 214without affecting the transmission of the incident beam 50.

In some embodiments, a reflective surface 110 may include two differentopenings, namely a detector opening and an optical source opening.

Accordingly, with the gas cell assembly 100B, versions of the incidentbeam 50, combined, travel a total path length of, at least, four timesthe length of the channel 106. The sensitivity of the absorptionmeasurements for the gas sample is, as a result of multipletransmissions of the optical beam within the channel 106, increased. Itwill be understood that the total path length shown in FIG. 2B is merelyfor ease of exposition and other total path lengths may similarly beprovided by the gas cell assembly 100B by adjusting the curvature ofeach of the reflective surfaces 110 f and 110 s, and a separationdistance between the reflective surfaces 110 f and 110 s.

FIG. 2C is a cross-sectional view of yet another gas cell assembly 100C.

Similar to the gas cell assembly 100B of FIG. 2B, the gas cell assembly100C also includes two reflective surfaces, namely a first reflectivesurface 110 f and a second reflective surface 110 s′. Unlike the gascell assembly 100B, the detector 114′ of the gas cell assembly 100C ispositioned to receive the last reflected beam 54 from the secondreflective surface 110 s via a detector opening (not shown) in thesecond reflective surface 110 s′. As shown, the optical source 112continues to be mounted on a mount 126′ to transmit an incident beam 50towards the first end portion 108 f via an optical source opening, suchas opening 214, at the first reflective surface 110 f. The detector 114′can be mounted on the base 132 using a mount 128.

Each of the first reflective surface 110 f and the second reflectivesurface 110 s′ may be provided as the reflective surface 210 shown inFIG. 3. When the reflective surface 210 is provided as the firstreflective surface 110 f′, the opening 214 can be provided as theoptical source opening. When the reflective surface 210 is provided asthe second reflective surface 110 s′, the opening 214 can act as thedetector opening for receiving the last reflected beam 54 and directingthe last reflected beam 54 towards the detector 114′. Also shown in FIG.3 is a series 212 of locations that received an optical beam andsubsequently reflected the received optical beam away towards the gascell body 102.

Referring again to FIG. 2C, as shown, the incident beam 50 is generatedby the optical source 112 and transmitted towards the first end portion108 f via the optical source opening (not shown) in the first reflectivesurface 110 f′. A version of the incident beam 50 is eventuallytransmitted through the second end portion 108 s and towards the secondreflective surface 110 s′, which then generates a first reflected beam52 towards the second end portion 108 s. Multiple reflected beams 52′,52″ and 52″′ can be generated before the last reflected beam 54 isreceived at the detector 114′. The number of reflected beams 52 shown inFIG. 2C is merely for ease of exposition and it will be understood thatother number of reflected beams 52 may be provided by the gas cellassembly 100C of FIG. 2C.

Generally, a separation distance between the first reflective surface110 f′ and the second reflective surface 110 s′ can be defined by aradius of curvature of the reflective surfaces 110 f′, 110 s′. The totalpath length of the versions of the incident beam 50 before the lastreflected beam 54 is received by the detector 114′ depends on, at least,the separation distance of the reflective surfaces 110 f′, 110 s′,and/or a position of the detector opening relative to the optical sourceopening. Therefore, varying a position of the detector opening can varythe total path length of the versions of the incident beam 50.

For example, when the reflective surface 210 of FIG. 3 operates as thesecond reflective surface 110 s′ of FIG. 2C, the opening 214 can operateas the detector opening. The detector opening defines which of thereceived optical beams in the series 212 is the last reflected beam 54.In the example shown in FIG. 3, the last reflected beam 54 is theoptical beam 216. To adjust the optical path, the detector opening 214can be rotated to intercept another one of the reflected beams in theseries 212 so that the other reflected beam, such as 216′, becomes thelast reflected beam 54. As a result of rotating the detector opening214, one or more of the optical beams in the series 212 may no longerappear on the reflective surface 210 due to the shortening of the totalpath length. It will be understood that the optical beams in the series212 are not formed consecutively and, therefore, to adjust the opticalpath in a controlled manner, the detector opening 214 may be rotated byvarying amounts.

FIG. 2D is a cross-sectional view of another example embodiment of thegas cell assembly 100C of FIG. 2C, or gas cell assembly 100C′.

Unlike the gas cell assembly 100C, the gas cell assembly 100C′ includesa temperature varying material 144 that substantially encloses thechannel 106. The temperature varying material 144 may be a heatingmaterial or a cooling material.

When the temperature varying material 144 is provided as a heatingmaterial, the heating material can be operated to cause a temperature ofthe channel 106 to increase and as a result, the temperature of the gassample within the channel 106 to also increase. The temperature varyingmaterial 144 may cause the temperature of the channel 106 to increaseabove an ambient temperature of the surrounding environment of the gascell assembly 100C. In some embodiments, the temperature of the channel106 may be increased by the heating material to be within a range ofapproximately 230° C. to 250° C. It will be understood that othertemperatures may similarly be applied depending on the type of gassample and/or analysis to be conducted on the gas sample.

When the temperature varying material 144 is provided as a coolingmaterial, the cooling material can be operated to cause a temperature ofthe channel 106 to decrease and as a result, the temperature of the gassample within the channel 106 to also decrease. In some embodiments, thecooling material may cause the temperature of the gas cell assembly 100Cto be decreased below the ambient temperature of the surroundingenvironment of the gas cell assembly 100C.

The material with which the channel 106 is formed can also control theamount of temperature change that can be provided by the temperaturevarying material 144.

As described, in some embodiments, the operation of the gas cellassembly 100C′ may be facilitated by increasing the temperature of thechannel 106. The increased temperature can reduce formation of ABS andas a result, significantly reduce ABS deposits from being formed on theinterior surfaces of the first and second end portions 108 f, 108 s andfrom clogging filters within the path of the gas sample. Also, since thetemperature varying material 144 only affects the temperature of the gascell body 102, the alignment of the optical components, namely the firstand second reflective surfaces 110 f′ and 110 s′, respectively, and theoptical source 112, are not affected.

As described, one or both surfaces of each of the first and second endportions 108 f and 108 s of the gas cell assembly 100C′ can include ananti-reflective material 140 f, 140 s, respectively. The anti-reflectivematerial 140 can reduce undesired reflections (and thus, also reducingoptical transmission losses) caused by the first and second end portions108 f and 108 s.

Also, a section of the first and second end portions 108 f and 108 s ofthe gas cell assembly 100C′ is coupled with a temperature varyingmaterial 142 f and 142 s, respectively. Similar to the temperaturevarying material 144, the temperature varying material 142 can operateto cause a temperature of the first end portion 108 f and the second endportion 108 s to increase. The temperature varying material 142 may helpto reduce any condensation in the gas sample at the first and second endportions 108 f and 108 s, which may affect the path of the optical beam.FIG. 4A illustrates an example end portion 240 for a gas cell assembly10.

The end portion 240 shown in FIG. 4A has a temperature varying material242 coupled to a substantially central location, generally shown as 244.In this example, the temperature varying material 242 is provided in acircular configuration. Other configurations of the temperature varyingmaterial 242 may be used, including a ring formation. The temperaturevarying material 242 may be a back-adhesive tape heat source in someembodiments.

When the temperature varying material 242 is provided on the end portion240, as shown in FIG. 4A, the corresponding reflective surface may beprovided as shown in FIG. 4B. FIG. 4B illustrates an example reflectivesurface 210′. The reflective surface 210′ is generally similar to thereflective surface 210 of FIG. 3 except that the reflective surface 210′includes a lead opening 218 for receiving leads for connecting thetemperature varying material 242 at the end portion 240 to a powersupply.

The lead opening 218 and the temperature varying material 242 can beprovided at a generally central location of the respective end portion240 and the reflective surface 210′ when the reflective surfaces 210 areprovided as concave mirrors. The concave mirrors may be sphericalmirrors. Concave spherical mirrors generally operate to reflect opticalbeams towards an outer radial perimeter. Therefore, the location of thelead opening 218 and the temperature varying material 242 at the centrallocation of the respective end portion 240 and the reflective surface210′ will unlikely affect the path of the optical beam in any of thedescribed embodiments.

Some embodiments of the gas cell assemblies described herein, such as 10and 100A to 100C′, can be operated within environments having differentpressures. For example, the gas cell assemblies 10 and 100A to 100C′ canbe operated in environments with a pressure that is below an ambientpressure of 760 Torr, such as approximately within a range of 10 Torr to700 Torr. At lower pressures, the gas cell assemblies 10 and 100A to100C′ may allow for increased sensitivity in the measured absorptionvalues.

FIGS. 5A and 5B illustrate example gas cell assemblies 500A and 500B,respectively. Each of the illustrated gas cell assemblies 500A and 500Bincludes a second reflective surface 510 s that includes twoneighbouring reflective surfaces, namely 510 s ₁ and 510 s ₂. Also, boththe optical source 112, 512 and the detector 114, 514 are positioned onthe same side of the gas cell assemblies 500A, 500B as the firstreflective surface 510 f, 510 f′, respectively.

As shown in FIG. 5A, the gas cell assembly 500A includes the firstreflective surface 510 f and the neighbouring reflective surfaces 510 s₁ and 510 s ₂. Similar to the gas cell assembly 100B of FIG. 2B, thefirst reflective surface 510 f is also positioned between the opticalsource 112 and the first end portion 108 f, as well as between thedetector 114 and the first end portion 108 f. To facilitate the passageof the incident beam 50 towards the first end portion 108 f and thepassage of the last reflected beam 54 from the first end portion 108 f,the first reflective surface 510 f, as shown in FIG. 5C, can include anoptical source opening 524 o and a detector opening 524 d, respectively.

Referring again to FIG. 5A, an example path of the incident beam 50 isillustrated. Generally, the neighbouring reflective surfaces 510 s ₁ and510 s ₂ can be configured to alternately reflect the one or moreversions of the incident beam 50 towards the gas cell body 102. In someembodiments, a first neighbouring reflective surface 510 s ₁ can bestacked on top of a second neighbouring reflective surface 510 s ₂. Thefirst neighbouring reflective surface 510 s ₁ may be placed directly ontop of the second neighbouring reflective surface 510 s ₂, or may beplaced on top of the second neighbouring reflective surface 510 s ₂ butwith a separation between the neighbouring reflective surfaces 510 s ₁and 510 s ₂.

For example, as shown in FIG. 5A, a version of the incident beam 50 canbe received by the first neighbouring reflective surfaces 510 s ₁, whichthen generates and directs a first reflected beam 52 towards the secondend portion 108 s. As the first reflective surface 510 f receives aversion of the first reflected beam 52, the first reflective surface 510f can then generate a second reflected beam 52′ towards the first endportion 108 f. A version of the second reflected beam 52′ can then bereceived by a second neighbouring reflective surface 510 s ₂ instead ofthe first neighbouring reflective surfaces 510 s ₁. The secondneighbouring reflective surfaces 510 s ₂ can then generate and direct athird reflected beam 52″ towards the second end portion 108 s. Althoughnot specifically shown in FIG. 5A, the first reflective surface 510 fand the neighbouring reflective surfaces 510 s ₁ and 510 s ₂ can operatein the described manner to continue increasing a total path length ofthe incident beam 50. The example first reflective surface 510 f shownin FIG. 5C illustrates an example series 522 of locations that receivedan optical beam and subsequently reflected the received optical beamtowards the gas cell body 102. FIG. 5B illustrates another example gascell assembly 500B. Similar to the gas cell assembly 500A of FIG. 5A,the gas cell assembly 500B includes a first reflective surface 510 f′and the neighbouring reflective surfaces 510 s ₁ and 510 s ₂. However,unlike the configuration of the gas cell assembly 500A, the firstreflective surface 510 f′ is not provided between the optical source 512and the first end portion 108 f, and between the detector 514 and thefirst end portion 108 f. Instead, the optical source 512 and thedetector 514 can be positioned away from the gas cell assembly 500B soas not to interfere with the path of each of the versions of theincident beam 50.

The optical source 512, as shown in FIG. 5B, can include a sourcedirecting surface 512 m for receiving an incident beam 50 from an opticgenerator 512 g and directing the received incident beam 50 towards thefirst end portion 108 f. The detector 514 can include a detectordirecting surface 514 m for receiving the last reflected beam 54 fromthe first end portion 108 f and directing the received last reflectedbeam 54 towards a detecting component 514 d. Each of the sourcedirecting surface 512 m and the detector directing surface 514 m caninclude a reflective surface, such as a mirror. The source directingsurface 512 m and the detector directing surface 514 m may also bepositioned substantially between the first reflective surface 510 f′ andthe first end portion 108 f.

With the source directing surface 512 m and the detector directingsurface 514 m, the first reflective surface 510 f′ does not requireopenings to facilitate passage of the incident beam 50 and the lastreflected beam 54. An example first reflective surface 510 f′ isillustrated in FIG. 5D.

Referring now to FIG. 6A, which is a perspective view of another examplegas cell assembly 600A.

Similar to the gas cell assembly 100C′ of FIG. 2D, the gas cell assembly600A includes an optical source 662 and a detector 664 positioned oneither ends of the gas cell assembly 600A. The optical source 662 inFIG. 6A can be configured to generate one or more different incidentbeams, such as first incident beam 650 m and a second incident beam 650s. As described, the optical source 662 can include multiple differentoptic generators that are either provided together as one unit or asseparate units. In some embodiments, the various different incidentbeams may be provided by splitting an incident beam generated by anoptic generator at the optical source 662.

The different incident beams, such as 650 m and 650 s, can be generatedby the optical source 662 and transmitted towards the gas cell body 102for identifying different gas components in the gas sample. In someembodiments, the gas sample can include, at least, a first gas componentwith a low absorption intensity level (e.g., ammonia) and a second gascomponent with a high absorption intensity level (e.g., moisture). Tofacilitate detection and measurement of the first gas component, the gascell assembly 600A can be configured to facilitate multiple passages ofan optical beam, such as the first incident beam 650 m, within the gascell assembly 600A to increase the sensitivity of the detection.

The second gas component, instead, can be already associated with a highabsorption intensity level and therefore, further increase in thesensitivity of the absorption intensity measurements may not berequired, or may possibly be undesired since increasing the sensitivityin the detection of the second gas component may saturate the resultingdata signal. For detecting and measuring the second gas component, thegas cell assembly 600A can be configured to facilitate a single passageof a corresponding optical beam, such as the second incident beam 650 s,within the gas cell assembly 600A.

As shown in FIG. 6A, the first reflective surface 610 f includes a firstoptical source opening 614 f and a second optical source opening 618 f,and the second reflective surface 610 s includes a first detectoropening 614 s and a second detector opening 618 s. FIG. 7A illustrates,at 710A, an example reflective surface 610. The reflective surface 710Acan include a first opening 614 (e.g., the first optical source opening614 f or the first detector opening 614 s) generally at a perimeter ofthe reflective surface 710A and a second opening 618 (e.g., the secondoptical source opening 618 f or the second detector opening 618 s)generally at a substantially central location of the reflective surface710A.

The first optical source opening 614 f can receive the first incidentbeam 650 m from the optical source 662 and direct the first incidentbeam 650 m towards the first end portion 608 f. The first incident beam650 m can proceed to be transmitted within the gas cell assembly 600A ina similar manner as the versions of the incident beam 50 described withrespect to FIGS. 2C and 2D. For example, when the second reflectivesurface 610 s receives a version of the first incident beam 650 m, thesecond reflective surface 610 s can then generate a first reflected beam652 m and direct the first reflected beam 652 m towards the second endportion 608 s. Upon receipt of a version of the first reflected beam 652m at the first reflective surface 610 f, the first reflective surface610 f can generate a second reflected beam 652 m′. An example series 612m of locations that received a version of the first incident beam 650 mis shown on the example reflective surface 710A in FIG. 7A.

At the end of the passage of the versions of the incident beam 650 m,the first detector opening 614 s can receive the version of the lastreflected beam 654 m from the second end portion 608 s and direct theversion of the last reflected beam 654 m towards the detector 664.

As described, the path of the second incident beam 650 s can be shorterthan the path of the first incident beam 650 m due to the difference inthe absorption intensity levels of the respective gas components forwhich the incident beams 650 s and 650 m are associated. Similar to thefirst optical source opening 614 f, the second optical source opening618 f can receive the second incident beam 650 s from the optical source662 and direct the second incident beam 650 s towards the first endportion 608 f. An example passage of a version of the incident beam 650s is shown generally as 612 s in FIG. 7A.

However, unlike the path of the first incident beam 650 m, when aversion of the second incident beam 650 s arrives at the secondreflective surface 610 s, the version of the second incident beam 650 sis not reflected by the second reflective surface 610 s and instead, theversion of the second incident beam 650 s (or the optical beam 654 s,which corresponds to the second incident beam 650 s) can be directed bythe second detector opening 618 s towards the detector 664. As shown inFIG. 6A, the second detector opening 618 s can be positioned relative tothe second optical source opening 618 f so as to prevent any reflectionof the version of the second incident beam 650 s at the secondreflective surface 610 s.

As shown in FIG. 7A, the path of the first incident beam 650 m(illustrated generally as 612 m) and the path of the second incidentbeam 650 s (illustrated generally as 612 s) do not interfere with eachother since the path of the first incident beam 650 m is generally alonga perimeter of the reflective surfaces 610 f, 610 s due to aconfiguration of the reflective surfaces 610 f, 610 s, while the path ofthe second incident beam 650 s is generally within a substantiallycentral portion of the reflective surfaces 610 f, 610 s.

The detector 664 can include multiple detector components that areconfigured for receiving different data signals. For example, in theillustrated example of FIG. 6A, the detector 664 can include a firstdetector component for receiving the last reflected beam 654 m from thefirst detector opening 614 s and a second detector component forreceiving the optical beam 654 s from the second detector opening 618 s.

In some embodiments, the gas cell assembly 600A may facilitate passageof two or more incident beams 650 that will undergo multiple reflectionswithin the gas cell assembly 600A. For example, the first incident beam650 m can include a first multi-pass incident beam and a secondmulti-pass incident beam. FIG. 7B illustrates generally at 710B anotherexample reflective surface 610 used for facilitating the path of thefirst multi-pass incident beam (illustrated generally as 612 m ₁) andthe path of the second multi-pass incident beam (illustrated generallyat 612 m ₂). Generally, the reflective surface 710B of FIG. 7B can besimilar to the reflective surface 710A of FIG. 7A except the reflectivesurface 710B receives two multi-pass incident beams. As shown in FIG.7B, the path 612 m ₂ of the second multi-pass incident beam can beradially offset from the path 612 m ₁ of the first multi-pass incidentbeam.

In some embodiments, the first and second multi-pass incident beams maybe received from different optical source components.

Similar to the gas cell assembly 100C′ of FIG. 2D, the first and secondend portions 608 f and 608 s, respectively, of the gas cell assembly600A can each include a temperature varying material 642 f and 642 s,respectively. It will be understood that the temperature varyingmaterial 642 f and 642 s are optional and are shown in FIG. 6A merelyfor illustrative purposes. In some embodiments, the first and second endportions 608 f and 608 s may be provided without the temperature varyingmaterial 642 f and 642 s, or one of the first and second end portions608 f and 608 s may be provided with the temperature varying material642 f and 642 s. The leads of the temperature varying material 642 f and642 s may also be coupled to the power supply via the second opticalsource opening 618 f and the second detector opening 618 s. That is, thesecond optical source opening 618 f and the second detector opening 618s may operate as lead openings 218.

Another example embodiment of a gas cell assembly 600B will be describedwith reference to FIG. 6B. Unlike the gas cell assembly 600A of FIG. 6A,the gas cell assembly 600B can facilitate passage of a second incidentbeam 650 d, as shown. Unlike the second incident beam 650 s of FIG. 6A,the second incident beam 650 d of FIG. 6B is a dual pass beam.

The gas cell assembly 600B can include an optical source for generatingthe one or more different incident beams, and a detector for receivingdata signals based on versions of the incident beams. As shown in FIG.6B, the optical source can be provided as a first optical sourcecomponent 662 a for generating the second incident beam 650 d and asecond optical source component 662 b for generating the first incidentbeam 650 m.

The detector in the gas cell assembly 600B can include a first detectorcomponent 664 a and a second detector component 664 b. The firstdetector component 664 a can receive the data associated with the lastreflected beam 654 m generated based on the first incident beam 650 m(similar to the detector 664 of FIG. 6A), while the second detectorcomponent 664 b can receive the data associated with the last reflectedbeam 654 d generated by a reflector component 660 based on the secondincident beam 650 d.

As shown in FIG. 6B, the reflector component 660 can be positioned at aside of the second detector opening 618 s that is opposite from thesecond end portion 608 s. The reflector component 660 can be configuredto receive a version of the second incident beam 650 d via the seconddetector opening 618 s from the second end portion 608 s, and to providethe reflected beam 652 d. The second detector component 664 b can,therefore, be configured for receiving the last reflected beam 654 dfrom the second optical source opening 618 f. The reflector component660 may generally be provided using any reflecting surface, such as, butwithout limitation, a plane mirror, a concave mirror, or a corner cube.

By including the reflector component 660, the second incident beam 650 dmay pass through the gas cell body 102 at least twice so that theresulting sensitivity of the measurements can be increased.

FIG. 8 is a block diagram of an example optical absorption spectroscopysystem 802 involving, at least, the gas cell assembly 100C′ of FIG. 2C.The optical absorption spectroscopy system 802 of FIG. 8 can operate asan extractive system.

The optical absorption spectroscopy system 802 is provided for acoal-burning power plant to measure an amount of ammonia in a gas sampleof flue gas. It will be understood that the optical absorptionspectroscopy system 802 may similarly be used for different applicationsIt will also be understood that the optical absorption spectroscopysystem 802 can involve any of the gas cell assemblies described hereinand that the gas cell assembly 100C′ is used and applied in FIG. 8 asonly an example.

The optical absorption spectroscopy system 802 includes an absorptionspectroscopy analyzer 16 for receiving data from the gas cell assembly100C′ and for providing control signals to the gas cell assembly 100C′.The absorption spectroscopy analyzer 16 may also send an incident beam,for example a laser beam of a desired wavelength, towards the opticalsource 112 for launching towards the gas cell assembly 100C′. As shownin FIG. 8, the analyzer 16 is in electronic communication with the gascell assembly 100C′. The analyzer 16 can send and receive data signalsfrom the gas cell assembly 100C′, such as the detector 114′ and theoptical source 112 via connectors 804, such as fiber-optic cables and/orcoaxial cables. The data signals may include analog data signals. Forexample, the detector 114′ may transmit data signals corresponding tothe last reflected beam 54 to the processing module 28 of the analyzer16 for conducting the relevant absorption spectroscopy analysis. It willbe understood that other forms of electronic communication may be used.Similarly, the analyzer 16 may provide control signals to the controllermodule 814 that is also in electronic communication with the gas cellassembly 100C′.

The inlet 104 i of the gas cell assembly 100C′ can receive the flue gasfrom the duct of the coal-burning power plant 18 via a vent opening,generally shown as 806. The inlet 104 i may receive the flue gas viadifferent components.

For example, in some embodiments, a sampling tube 826 may couple theinlet 104 i to the gas source 18. The sampling tube 826 can be insertedinto the vent opening 806. The sampling tube 826 may attain thetemperature of the gas sample in some embodiments. The length of thesampling tube 826 may vary depending on the size of the gas source 18and/or the analysis to be conducted. The sampling tube 826 may also haveseveral openings (not shown) for receiving the flue gas from the gassource 18. The openings in the sampling tube 826 may be separated fromeach other by a certain distance along the length and width of thesampling tube 826. The openings on the sampling tube 826 may also havedifferent sizes depending on the analysis to be conducted on the gassample and/or the gas source 18.

In some embodiments, a filter 820 may also be included into the samplingtube 826. The filter 820 can interact with an initial gas sample fromthe gas source 18 to remove dust and/or certain contaminants to generatethe gas sample for the gas cell assembly 100C′. During the interaction,the filter 820 may increase in temperature. The filter 820 may attainthe temperature of the gas sample in some embodiments. The filter 820may be a ceramic filter or other suitable filter that is operable athigh temperatures. The ceramic filter or other suitable filter can beassociated with pore sizes that are appropriate for the gas sample.

In embodiments in which the filter 820 is provided, the inlet 104 i mayalso be coupled to the sampling tube 814 with a multi-directional valve810. The multi-directional valve 810 can be operated by the controllermodule 814. For example, the controller module 814 may operate themulti-directional valve 810 in a first position so that themulti-directional valve 810 provides a path between the gas source 18and the inlet 104 i so that the flue gas can enter the channel 106. Thecontroller module 814 may also operate the multi-directional valve 810in a second position to provide a path between an external gas line 812and the gas source 18 so that a pressurized gas can be sent from theexternal gas line 812 towards the gas source 18 for cleaning the filter820. The controller module 814 may operate the multi-directional valve810 in the second position at predefined time periods and/or in responseto a control signal provided by the analyzer 16 indicating the filter820 requires cleaning.

In some embodiments, the external gas line 812 may be coupled with theinlet 104 i in a further position of the multi-directional valve 810 forpurging the gas sample and other particles from the channel 106.

When the flue gas is received into the channel 106 via the inlet 104 i,a pump 822 may be coupled to the outlet 104 o for directing the flue gasthrough the channel 106 towards the outlet 104 o. The pump 822 may be inelectronic communication with the controller module 814. For example,when the multi-directional valve 810 is at the first position (a gassample is being received at the inlet 104 i), the pump 822 can beactivated by the controller module 814 to direct the gas sample towardsthe outlet 104 o. However, when the multi-directional valve 810 is atthe second position (the external gas line 812 is sending pressurizedgas towards the filter 820), the pump 822 can be turned off by thecontroller module 814. The pump 822 may be coupled to the controllermodule 814 with an alternating current contactor, and the alternativecurrent contactor can operate to turn the pump 822 on or off, dependingon the operation of the multi-directional valve 810.

Also, a heat source controller 824 may also be provided to control thetemperature of the temperature varying material 144 that substantiallyencloses the channel 106.

Referring now to FIG. 9, which is a block diagram of another exampleoptical absorption spectroscopy system 902 involving, at least, the gascell assembly 100C′ of FIG. 2C. Similar to the optical absorptionspectroscopy system 802 of FIG. 8, the optical absorption spectroscopysystem 902 of FIG. 9 can also operate as an extractive system.

The optical absorption spectroscopy system 902, like the opticalabsorption spectroscopy system 802 of FIG. 8, is provided for acoal-burning power plant to measure an amount of ammonia in a gas sampleof flue gas. It will be understood that the optical absorptionspectroscopy system 902 may be used for different applications. It willalso be understood that the optical absorption spectroscopy system 902can involve any of the gas cell assemblies described herein and that thegas cell assembly 100C′ is used and applied in FIG. 9 as only anexample.

Like the optical absorption spectroscopy system 802 of FIG. 8, theabsorption spectroscopy system 902 also includes the absorptionspectroscopy analyzer 16 for receiving data from the gas cell assembly100C′ and for providing control signals to the gas cell assembly 100C′,and can also receive the flue gas from the duct of the coal-burningpower plant 18 via a sampling tube 826 inserted into the vent opening806. It will be understood that the inlet 104 i may receive the flue gasvia different components. The absorption spectroscopy system 902 alsoincludes a heat source controller 824 for controlling the temperature ofthe temperature varying material 144 that substantially encloses thechannel 106.

Unlike the optical absorption spectroscopy system 802, the opticalabsorption spectroscopy system 902 includes a pressure measuringcomponent 928 for monitoring a pressure of the gas sample within thechannel 106, and a filter 920 outside the vent opening 806. By providingthe filter 920 outside of the vent, the filter 920 can be moreaccessible and thus, can facilitate cleaning and/or replacement.

The pressure measuring component 928 can, in some embodiments, operateto determine whether the filter 920 is clogged and requires cleaning.The pressure measuring component 928 may be a pressure gauge. Forexample, when the pressure measuring component 928 detects that the gassample within the channel 106 is below a minimum pressure threshold, thepressure measuring component 928 can determine that a surface of thefilter 920 is covered with particulates such that the pressure of thegas sample is affected and therefore, the filter 920 requires cleaning.In response to the determination by the pressure measuring component 928that the pressure of the gas sample within the channel 106 is below theminimum pressure threshold, the controller module 914 can then activatea first valve 910 a to clear the surface of the filter 920. As shown inFIG. 9, the first valve 910 a is operably coupled to the filter 920 sothat, when activated by the controller module 914 for cleaning thesurface of the filter 920, the first valve 910 a facilitates passage ofan external high pressure air to interact with the surface of the filter920 for releasing the particulates.

The pump 922 in the embodiment shown in FIG. 9 can be provided as a jetpump. Similar to the pump 822, the pump 922 can, in conjunction with asecond valve 910 b, direct the flue gas through the channel 106 towardsthe outlet 104 o. Similar to the channel 106, the connection lines ofthe pump 922 may be heated to a range of approximately 230° C. to 250°C. The increased temperature can reduce formation of ABS and as aresult, significantly reduce ABS deposits from being formed on theinterior surfaces of the pump 922.

The first and second valves 910 a and 910 b may, in some embodiments, besolenoid valves. It will be understood that other types of valves thatcan function in the similar fashion as described with respect to thefirst and second valve 910 a and 910 b can also be used.

As shown in and described with reference to FIG. 9, instead of using themulti-directional valve 810, the first and second valves 910 a and 910 bcan be included into the optical absorption spectroscopy system 902 fordirecting gas and air flow.

Various embodiments have been described herein by way of example only.Various modification and variations may be made to these exampleembodiments without departing from the spirit and scope of theinvention, which is limited only by the appended claims.

We claim:
 1. An absorption spectroscopy system comprising: an opticalsource for transmitting an incident beam; a gas cell assembly having: aninlet for receiving a gas sample from a gas source; an outlet forreleasing the gas sample from the gas cell assembly; a channel coupledto the inlet and the outlet, the channel providing a path for at leastthe incident beam and the gas sample; and a detector positioned relativeto the channel for receiving a reflected beam corresponding to a versionof the incident beam, the detector being operable to transmit a datasignal corresponding to the reflected beam; an absorption spectroscopyanalyzer in electronic communication with the gas cell assembly, theanalyzer comprising: a communication component operable to receive thedata signal from the detector; and a processor operable to conduct theabsorption spectroscopy analysis of the gas sample based on the datasignal; and a controller in electronic communication with the absorptionspectroscopy analyzer and the gas cell assembly, wherein the controllerreceives control signals from the absorption spectroscopy analyzer foroperating the gas cell assembly.
 2. The system of claim 1, wherein: thegas cell assembly comprises: a gas cell body having: a first end portionalong a longitudinal axis of the body, the first end portion allowingoptical transmission into and out of the body, and the first end portionreceiving the incident beam from the optical source; and a second endportion substantially opposite from the first end portion, the secondend portion allowing the optical transmission into and out of the body;one or more reflective surfaces positioned outside the body, the one ormore reflective surfaces including a reflective surface substantiallyopposite from the second end portion, the one or more reflectivesurfaces receiving one or more versions of the incident beam from thebody and reflecting at least one of the one or more versions of theincident beam towards the body; the channel providing the path betweenthe first end portion and the second end portion; and the detector beingpositioned relative to one of the first end portion and the second endportion for receiving the reflected beam from the one or more reflectivesurfaces.
 3. The system of claim 2, wherein the one or more reflectivesurfaces comprises: a first reflective surface substantially oppositefrom the first end portion, the first reflective surface having anoptical source opening for receiving the incident beam from the opticalsource and directing the incident beam towards the first end portion;and a second reflective surface substantially opposite from the secondend portion, the second reflective surface having a detector opening forreceiving the reflected beam from the second end portion and directingthe reflected beam towards the detector.
 4. The system of claim 2,wherein the one or more reflective surfaces comprises a first reflectivesurface substantially opposite from the first end portion and a secondreflective surface substantially opposite from the second end portion;and at least one of: the optical source comprises a source directingsurface for receiving the incident beam from the optical source anddirecting the incident beam towards the first end portion, the sourcedirecting surface being positioned substantially between the firstreflective surface and the first end portion; and the detector comprisesa detector directing surface for receiving the reflected beam from thefirst end portion and directing the reflected beam towards the detector,the detector directing surface being positioned substantially betweenthe first reflective surface and the first end portion.
 5. The system ofclaim 2, wherein the one or more reflective surfaces comprises a firstreflective surface substantially opposite from the first end portion anda second reflective surface substantially opposite from the second endportion, the first reflective surface having: an optical source openingfor receiving the incident beam from the optical source and directingthe incident beam towards the first end portion; and a detector openingfor receiving the reflected beam from the first end portion anddirecting the reflected beam towards the detector.
 6. The system ofclaim 2, wherein: at least one of the one or more reflective surfaceshas a lead opening at a substantially central location; and a section ofat least one of the first end portion and the second end portion iscoupled with a temperature varying material, the temperature varyingmaterial is coupled to a power supply with one or more leads, and thelead opening receiving the one or more leads.
 7. The system of claim 1further comprises a pump coupled to the outlet for directing the gassample into the inlet and out of the outlet.
 8. The system of claim 7,wherein the pump comprises a jet pump.
 9. The system of claim 1 furthercomprises a sampling tube having one end coupled to the inlet, and thesampling tube being inserted into a vent opening of the gas source. 10.The system of claim 9 further comprises a multi-directional valvemounted between the sampling tube and the inlet, wherein themulti-directional valve is operable by the controller in a firstposition to provide a path between the gas source and the inlet, and ina second position to provide a path between an external gas line and thegas source.
 11. The system of claim 9 further comprises a filter mountedwithin the sampling tube to remove contaminants from the initial gassample.
 12. The system of claim 11 further comprises a multi-directionalvalve mounted between the sampling tube and the inlet, wherein themulti-directional valve is operable by the controller in a firstposition to provide a path between the gas source and the inlet, and ina second position to provide a path between an external gas line and thegas source in response to receiving a control signal from the absorptionspectroscopy analyzer indicating the filter requires cleaning, the pathbetween the external gas line and the gas source directing a pressurizedgas from the external gas line towards the filter.
 13. The system ofclaim 11, wherein the filter is suitable for high temperatureenvironments.
 14. The system of claim 9 further comprises a filtermounted outside the vent opening to remove contaminants from the initialgas sample.
 15. The system of claim 14, wherein the filter is suitablefor high temperature environments.
 16. The system of claim 14 furthercomprises: a pressure sensor coupled to the inlet, the pressure sensormonitoring a pressure within the gas cell assembly; and a first valveoperable by the controller to provide a path between an external gasline and the filter in response to receiving an activation signalgenerated by the pressure sensor when a value of the pressure is lessthan a minimum pressure threshold.
 17. The system of claim 1, whereinthe gas source is a power generation plant.
 18. The system of claim 1,wherein the absorption spectroscopy analyzer is in electroniccommunication with the gas cell assembly via at least one of (i) one ormore fiber optic cables and (ii) one or more coaxial cables.
 19. Thesystem of claim 1, wherein the controller comprises a relay circuitry.20. The system of claim 1, wherein a wavelength of the incident beamvaries according to the absorption spectroscopy analysis being conductedon the gas sample.